An apparatus including: a current source configured to generate current; a bias node coupled to the current source; a switching current source circuit coupled to the current source and the bias node to allow the current to flow through the switching current source circuit into the bias node; a biasing circuit configured to receive a control signal from a phase detector, and mirror the current flowing through the switching current source circuit in response to the control signal; and a switch device disposed between the switching current source circuit and the biasing circuit to isolate the switching current source circuit from the biasing circuit.